Stage 1: Preliminary assessment of mean flow rate and its inter-subject variability, and a comparison to IV infusion. Each subject will receive a SC infusion of 400 mL (from a 0.5 L bag) of Ringer’s lactate solution in each upper arm, followed by one IV infusion of 400 mL of Ringer’s lactate solution (from a 0.5 L bag). The SC injection sites will be randomized in a double-blinded fashion to receive either 150 units Hylenex or an equal volume of saline placebo injected into a Y-port in the tubing just above the catheter immediately prior to infusion. 24-gauge angiocatheters will be placed symmetrically in the SC space in both proximal upper extremities at the lateral aspect, midline halfway between the olecranon process and the inferoposterior aspect of the acromion, introduced at a 30-degree angle. A 24-gauge angiocatheter will also be placed in a vein in either the left or right forearm (per randomization). In each upper arm, Ringer’s lactate solution will be infused SC by gravity (wide open) by placing the top of the fluid in a 0.5 liter bag at a height of 100 cm above the respective angiocatheter sites. After completion of both SC infusions, Ringer’s lactate solution will be infused IV by gravity (wide open) by placing the top of the fluid in a 0.5 liter bag at a height of 100 cm above the angiocatheter sites. The flow rate observations in Stage 1 will be used to either confirm or adjust the proposed sample size for Stage 2, if such adjustment is necessary.